Focal Planes (FPA) consist of a compound semiconductor sensing element (i.e., detector) and a silicon readout array (i.e., CMOS read-Out Integrated Circuit (ROIC)) joined on a pixel by pixel level. In infrared sensing systems that utilize flip chip assemblies of FPAs, indium bump technology is used to bond the detector array to the ROIC. Specifically, each of the detector array and the ROIC include indium bumps formed on the surface thereof. The indium bumps on the opposing surfaces of each device may be mated and joined together in a process called hybridization.
Although indium has proved to be a good material for these applications, layers of native oxide may be formed on the indium bumps during the fabrication of the FPA. The native oxide may prevent proper interconnection between the detector array and ROIC. As the number of pixels increases and the sizes of the pixels decreases, the formation of native oxide on indium bumps may pose significant challenges. As such, the native oxide must be removed prior to the hybridization process.
Known techniques for removing the native oxide include a mechanical scrubbing process that includes rubbing the mated indium bumps against each other until the oxide layer breaks. This process may impose harmful mechanical stress on chip contacts and have a negative impact on yield. For example, as the surface area of the detector array increases, the force that is required to break through the oxide increases exponentially and may exceed the limits that may be withstood by commercially available devices. As a result, mechanical scrubbing may induce crystal damage and have detrimental effects on device performance. Other known techniques include the use of cleaning agents or acid etches that may also cause corrosion and/or degradation of the indium. Accordingly, known techniques for chemically or mechanically removing the native oxide layers may result in damage to FPA components and the fabrication of defective circuits.